The present invention relates to warning systems for providing a warning when two vehicles are near a common collision point. For example, the present invention relates to a system for providing a warning when a vehicle and a train simultaneously are near a common railroad crossing.
Almost as long as railroad crossings have been in existence, efforts have been made to prevent vehicles from running into or being hit by trains at the railroad crossings. At least as early as the 1930's, efforts have been made to employ radio control devices to improve the safety of railroad crossings. Previous systems, however, were subject to false alarms. False alarms would be generated, for example, whenever a vehicle and a train were in proximity to each other without regard to them both being in proximity to a common railroad crossing. In addition, a false alarm would be generated when, for example, a vehicle received a radio frequency that was generated by a source other than safety equipment on the train. Such a stray or erroneous signal could be generated by another transmitter or could be radio frequency noise.
In addition, previous systems did not have the capability of closed loop verification. For example, an engineer on a train would not know if the train was actually transmitting the proper frequency and if equipment at a railroad crossing was operating properly. Without such verification, it is impossible to determine whether or not any vehicles approaching a railroad crossing could possibly be warned.
In addition to overcoming the technical drawbacks of prior systems, there is a significant economic need for a simple, economic and reliable railroad crossing warning device. A 1975 study prepared for the U.S. Department for Transportation entitled "Feasibility Study of In-Vehicle Warning System" (DOT HS-801 569) indicates that there are approximately 12,000 railroad crossing accidents annually. These accidents result in tremendous costs to society in terms of lost lives, medical payments and increased expenses for railroads.